In small gas turbine engines, it is known that high altitude starting is limited by poor fuel atomization and poor fuel distribution particularly where swirl pressure atomizing fuel injectors are utilized. It has subsequently been found by me that better atomized and distributed fuel, and thus significantly enhanced high altitude starting, can be obtained by the use of pressure impingement fuel injectors which prove to be far more efficient (see my commonly owned and copending patent application Ser. No. 652,010, filed Feb. 7, 1991.) As a further benefit, the complexities, costs and unreliabilities of current start injectors can be eliminated, i.e., ignition can be obtained from a main fuel injector without resort to a start injector.
However, as is well known, altitude starting can be seriously inhibited by reason of chemical kinetics even with good fuel atomization and distribution. Specifically, given a sufficiently high altitude, combustion may not occur because the dome height (and, thus, the combustor volume) is too small. In order to overcome this problem, I have previously disclosed the concept of simulating a relative large volume in a combustor of low dome height by staging fuel injection.
Of course, it is known to be desirable to minimize the number of fuel injectors in small gas turbine engines. In this connection, it is well known that injectors are costly and, where a high number of fuel injectors is required, there will be a resulting low fuel flow per injector which means that the injectors are much more prone to clogging or plug-up. Furthermore, in many instances, small scale viscous effects deteriorate fuel atomization at such reduced fuel flows.
As will be appreciated, when such a condition exists, it is most difficult to achieve a satisfactory level of combustion. This is a particular problem at the low fuel flow rates associated with high altitude starting which might otherwise be overcome if the combustor could be sized sufficiently large to provide additional time for fuel evaporation and combustion therewithin. However, in many instances, it is simply impossible to provide the necessary space for utilization of a combustor of sufficient volume.
As previously mentioned, the desired combustor volume might nevertheless be obtainable for some specific applications. This can be achieved, for instance, by extending the combustor length to account for the limit on dome height. However, it has been determined that this technique does not always successfully result in the desired operating characteristics.
The present invention is directed to overcoming one or more of the foregoing problems and achieving one or more of the resulting objects by further enhancing performance in compact combustors at ultra high altitudes.